This study involves a subset of T-cells, the gamma-delta T- cells, whose existence was unknown less than a decade ago. Although the function of gamma/delta T-cells in the immune system is still unclear, recent advancements in the field indicate that these cells may be vitally important in some disease conditions. The broad, long-term objective of the study described in this application is to understand the immunological function of gamma-delta T-cells, focusing on the nature of antigen recognition in these cells. The hypothesis is that gamma/delta T-cells, though similar to the long-studied alpha/beta T- cells in many respects, exist as a distinct, evolutionarily conserved subset because they provide a unique immune function directly related to their mechanism of antigen recognition. This study proposes to investigate this question through the following specific aims: 1. To determine which portions of the TCR expressed by HSP-60 reactive gamma/delta T-cells directly contact the stimulatory ligand. 2. To investigate whether a presenting molecule is involved in antigen recognition by a group of gamma-delta T-cells, the HSP-60 reactive subset. 3. To investigate the functional abilities of normal HSP-60 reactive gamma/delta T- cells. 4. To examine the biological role of HSP-60 reactive gamma/delta T- cells in a bacterial infection model.